I would call Southern Mattress in Rocky Mt. NC. and ask, they make mattresses for both trailers. They also make different thickness mattress so you want to be aware of that. I had one DLX Southern mattress that was about 10" thick. Ikea sells a full size foam mattress that has a zippered opening cover. I unzip it and trim the corners off the foam with an elec. carving knife and tuck the loose cover corners in the rear corners of the trailer. The Ikea mattress is a much less expensive option.
Eddie

We found the standard Scamp foam on our 2017 Scamp 16 Deluxe to be
too firm/hard for sleeping.

We went to a local foam/upholstery shop and replaced the new/original
Scamp foam with cushions made with a 3-layer foam sandwich
(1 inch of medium density foam glued to the top and bottom of
a 2 inch thickness of higher density foam).
Now, we sleep much better.

The cost was around $200. I figured that was about the cost of a mattress
and/or an additional mattress topper.

Although we typically leave the dinette in bed configuration, we do still have the option, in inclement weather, of converting back to a dinette for
card/board games or an indoor meal for more people.

I have the mattress from Southern Mattress. We like it very much and I find it better to sleep on than the expensive mattresses in our home. It cost us about $700 or so, if I recall correctly.

However, after we bought this I talked to a local mattress retailer and he said he could order a custom mattress if the could make a pattern. So you may want to also consider going to a local mattress retailer.

I like Ray's idea with the cushions. This seems like a very outstanding way to solve the issue of the original cushions being too hard. Now why did I not think of this solution?

Don.t waste your time looking for a ready made mattress. I had one made bt Texas Mattress Maker in Houston TX. It cost around $450.00 but worth every penny. It is great to sleep on and fit the back of Scamp like a glove.

I would suggest that you have the mattress made in two parts to make it easier to handle when you need to get into the bench area. I had the matress made in 2 halves with handles on all four side.

I found a thick "memory" foam mattress and cut it to fit. It is two layers of foam of different firmness. I cut/sawed it to fit with a cheap bread knife from the thrift store. Works great but the added height takes some getting used to. I have to jump up on the bed now! I do second the idea of two pieces though. It was quite the sight/fight getting the one-piece mattress in the back of the Scamp by myself. Of course there was not room for anybody else to help anyway. Ever see a piece of foam kick a grown man's behind? I get my revenge every night I get a good night's sleep on it however.

We did what Tim did before we bought the Southern Mattress. We had three layers of foam of varying densities. It was quite comfortable but having cut it with a sharp knife the layers were uneven and the shape irregular; it was unsightly so we bought the Southern Mattress.

Perhaps an electric knife might be better that just a sharp knife. But Patrice on a piece of throwaway foam until you get the hang of it.